📝 spec(renderer): specify caret behavior at wrap boundaries

Author: cowboyd

specs/renderer-spec.md

@@ -354,6 +354,14 @@ offset `N`:
 - If `N > [...content].length` or `N < 0`, behavior is unspecified; callers must
   keep offsets within bounds.
 
+When the layout engine consumes whitespace at a wrap boundary — dropping it
+from the rendered text so that neither wrapped line contains a display cell for
+those code points — the caret has no display position of its own for any offset
+that falls in that dropped run. In that case the caret's cell is the origin of
+the following wrapped line (the display position of the first code point on
+that line). This rule keeps the caret on-screen at the point where subsequent
+input will land, rather than orphaning it past the end of the previous line.
+
 When `content` is empty, the only in-range offset is `0`. In that case the
 caret's cell is the text element's origin — the cell at which the first code
 point of `content` would be drawn if `content` were a single space. This is a